Age 30
Seen August 16th, 2019
Posted February 8th, 2019
416 posts
6.8 Years
Image data like that is LZSS compressed. You can either implement your own given the spec on GBATek or use this library.
SWI 11h (GBA/NDS7/NDS9) - LZ77UnCompWram
SWI 12h (GBA/NDS7/NDS9) - LZ77UnCompVram (NDS: with Callback)
Expands LZ77-compressed data. The Wram function is faster, and writes in units of 8bits. For the Vram function the destination must be halfword aligned, data is written in units of 16bits.
If the size of the compressed data is not a multiple of 4, please adjust it as much as possible by padding with 0. Align the source address to a 4-Byte boundary.
r0 Source address, pointing to data as such:
Data header (32bit)
Bit 0-3 Reserved
Bit 4-7 Compressed type (must be 1 for LZ77)
Bit 8-31 Size of decompressed data
Repeat below. Each Flag Byte followed by eight Blocks.
Flag data (8bit)
Bit 0-7 Type Flags for next 8 Blocks, MSB first
Block Type 0 - Uncompressed - Copy 1 Byte from Source to Dest
Bit 0-7 One data byte to be copied to dest
Block Type 1 - Compressed - Copy N+3 Bytes from Dest-Disp-1 to Dest
Bit 0-3 Disp MSBs
Bit 4-7 Number of bytes to copy (minus 3)
Bit 8-15 Disp LSBs
r1 Destination address
r2 Callback parameter (NDS SWI 12h only, see Callback notes below)
r3 Callback structure (NDS SWI 12h only, see Callback notes below)
Return: No return value.

Its not too complicated... but what do MSBs and LSBs mean?

Ive seen dsdecmp before but it does not seem to work like I want (cant get output to image) or im messing up somewhere else, could be anything... who knows